This invention relates generally to high pressure decorative laminates and methods for producing same, and more specifically, laminates having a deeply textured surface displaying a tile design.
Typically deeply textured embossed high pressure decorative laminates are produced with an overall thickness greater than those with more planar textures, such that the areas of deepest embossment have a thickness about the same as that for conventionally textured high pressure decorative laminates. While this avoids the problem of texture embossment punch-through and weakening of the laminate structure, with associated breakage, etc., the necessary increased thickness of such laminates detracts from their postformability. As such, it is often not possible to postform these laminates to the relatively tight radii of conventional kitchen countertop profiles, or other demanding postforming applications, and therefore restricting their use to either general purpose flatstock applications, or postforming applications with less aesthetically pleasing larger radii bends. For the aforementioned reasons, a deeply embossed tile design high pressure decorative laminate, with commercially acceptable physical properties and postforming characteristics, has been heretofore precluded.
High pressure decorative laminates have been used as a surfacing material for many years, in commercial and residential applications, where pleasing aesthetic effects, in conjunction with functional behavior, such as superior wear, heat and stain resistance compared to alternative surfacing materials, have been desired. Typical applications include, but are not limited to, furniture, kitchen countertops, table tops, store fixtures, bathroom vanity tops, cabinets, wall paneling, partitions, and the like. However, historically, high pressure decorative laminates have not been successfully used to replace xe2x80x9cnaturalxe2x80x9d ceramic tile for applications such as kitchen countertops, bathroom vanity tops, or shower and tub surrounds, where the xe2x80x9crealxe2x80x9d tile look is desired, even though high pressure decorative laminate offers several distinct advantages over ceramic tile, including a naturally antibacterial, antifungal and mold resistant surface, ease of installation, ease of cleaning, lower cost, warmth to the touch, and more forgiveness with breakable objects such as glassware and dinnerware. A natural ceramic tile installation consists of 5% or more porous grout area, which is easily stained and readily promotes bacterial, fungal and mold growth, which is becoming ever more of a household and business concern. Therefore, the need exists for a postformable, high pressure decorative laminate with a pleasing, deep textured tile design simulating the look and feel of natural ceramic tile without the deficiencies noted above.
High pressure decorative laminates can generally be classified by their decorative surface design as being either a uniform solid color, or a printed pattern, whether a woodgrain, stone-like or abstract design. Each type of high pressure decorative laminate can also be classified as to its surface finish, which in conjunction with its color or pattern, contributes to the overall decorative surface design, structure and aesthetics, as will be discussed in more detail below. High pressure decorative laminates can also be classified by their intended application as defined by the industry""s governing body, the National Electrical Manufacturers Association (NEMA) in there standards publication LD 3-1995. Of particular interest is the xe2x80x9cpostforming typexe2x80x9d, which is defined as xe2x80x9ca high pressure decorative laminate (HPDL) similar to the general-purpose type, but is capable of being thermoformed under controlled temperature and pressurexe2x80x9d after its initial manufacture, which is well understood by those versed in the art.
High pressure decorative laminates are generally comprised of a decorative sheet layer, which is either a solid color or a printed pattern, over which is optionally placed a translucent overlay sheet, typically employed in conjunction with a print sheet to protect the print""s ink line and enhance abrasion resistance, although an overlay can also be used to improve abrasion resistance of a solid color as well. A solid color sheet typically consists of alpha cellulose paper containing various pigments, fillers and opacifiers, generally with a basis weight of about 50 to 120 pounds per 3000 square foot ream. Similarly, print base papers are also pigmented and otherwise filled alpha cellulose sheets, usually lightly calendered and denser than solid color papers, and lower in basis weight at about 40-75 pounds per ream, onto which surface is rotogravure or otherwise printed a design using one or more inks. Conversely, overlay papers are typically composed of highly pure alpha cellulose fibers without any pigments or fillers, although they can optionally be slightly dyed or xe2x80x9ctintedxe2x80x9d, and are normally lighter in weight than the opaque decorative papers, in the range of 10-25 pounds per ream.
Typically, these overlay and decorative print and solid color surface papers are impregnated, or xe2x80x9ctreatedxe2x80x9d, with a melamine-formaldehyde thermosetting resin, which is a condensation polymerization reaction product of melamine and formaldehyde, to which can be added a variety of modifiers, including plasticizers, flow promoters, catalysts, surfactants, release agents, or other materials to improve certain desirable properties, as will be understood by those versed in the art. As with melamine-formaldehyde resin preparation and additives thereto, those versed in the art will also appreciate that other polyfunctional amino and aldehydic compounds can be used to prepare the base resin, and other thermosetting polymers, such as polyesters, may be useful as the surface resin for certain applications, but use of a melamine-formaldehyde resin is preferred. Optionally, an untreated decorative paper can be used in conjunction with a treated overlay, if the overlay contains sufficient resin, such that during the laminating process heat and pressure consolidation, there is adequate flow of the resin from the overlay to contribute to the adjacent decorative layer, so as to effect sufficient interlaminar bonding of the two, as well as bonding of the decorative layer to the core. The equipment used to treat these various surface papers is well known to those versed in the art. The papers are normally treated to controlled, predetermined resin contents and volatile contents; the optimum levels will be well understood by those versed in the art, with typical resin contents in the ranges of 64-80%, 45-55% and 35-45% for overlay, solid color and print (unless used untreated) papers respectively, and all with volatile contents of about 5-10%.
The surface paper of a high pressure decorative laminate is simultaneously bonded to the core, which usually is comprised of a plurality of saturating grade kraft paper xe2x80x9cfillerxe2x80x9d sheets, which have been treated or impregnated with a phenol-formaldehyde resin, which also simultaneously fuse and bond together during the laminating process, forming a consolidated, multi-lamina integral assembly. Again, those versed in the art will appreciate that a variety of modifiers such as plasticizers, extenders and flow promoters can be added to the phenol-formaldehyde resin, that other phenolic and aldehydic compounds can be used to prepare the base resin, or other types of thermosetting resins such as epoxies or polyesters may be used, although a phenol-formaldehyde resin is preferred. In addition, other materials such as linerboard, fabric, glass, or carbon fiber may be used for the filler plies, but a saturating grade kraft paper and other modified kraft papers are presently preferred, typically with a basis weight of about 70-150 pounds per ream. The resin preparation and filler treating methodologies are also well known to those versed in the art.
During the laminating or pressing operation, the various surface and filler sheets are cured under heat and pressure, to fuse and bond them together, consolidating them into an integral mass. Typically, this process is accomplished in a multi-opening, flat bed hydraulic press between essentially inflexible, channeled platens capable of being heated and subsequently cooled. While other types of press equipment can be used to produce high pressure decorative laminates, for example a continuous double belt press, a single or limited opening xe2x80x9cshort cyclexe2x80x9d press, or an isothermal xe2x80x9chot dischargexe2x80x9d press, a conventional multi-opening press is most suited to the practice of the present invention.
Typically, back-to-back pairs of laminate assemblies, consisting of a plurality of filler sheets and one or more surface sheets, are stacked in superimposed relationship between rigid press plates, with the surfaces adjacent to the press plates. Such press plates are typically made of a stainless steel alloy such as AISI 410, and can have a variety of surface finishes, which they either impart directly to the laminate surface during the pressing operation, or they are used in conjunction with a non-adhering texturing/release sheet between the laminate surface and the plate, which will impart a finish to the laminate surface as well. Such texturing/release sheets, for example paper backed aluminum foil, or a variety of polymer coated papers, are commercially available from a variety of suppliers.
Several pairs of laminate assemblies are usually interleaved between several press plates to form a press pack (or book), which is then inserted, by means of a carrier tray, into an opening or xe2x80x9cdaylightxe2x80x9d between two of the heating/cooling platens of the multi-opening, high pressure flat bed press. The press platens are typically heated by direct steam, or by high pressure hot water, the latter usually in a closed-loop system, and water cooled. The laminate pairs between the press plates are usually separated from each other by means of a non-adhering material such as a wax coated paper, or biaxially oriented polypropylene film, which are commercially available, or the backmost face of one or both of the laminates"" opposed filler sheets in contact with each other is coated with a release material such as a wax or fatty acid salt. In either case, after the pressing operation has been completed and the press pack removed from the press, the press plates are removed sequentially from the press pack build-up, and the resultant laminate doublets separated into individual laminate sheets. In a separate operation, these must then be trimmed to the desired size, and back sanded so as to improve adhesion during subsequent bonding to a substrate and other fabrication.
A typical press cycle, once the press is loaded with one or more packs containing the laminate assemblies and press plates, will consist of closing the press to develop a specific pressure of about 1000-1500 psig, heating the packs to about 130-145 C., holding at that temperature for a predetermined time, and then cooling the packs to or near room temperature before discharging the packs from the press for separation. Those versed in the art should have a detailed understanding of the overall pressing operation, and will recognize that careful control of the degree of the laminate""s cure, as well as its cure temperature, are critical in achieving the desired laminate properties, particularly its postformability, as are selection of the proper melamine-formaldehyde and phenol-formaldehyde surface and filler resins respectively, as well as the surface and filler paper properties.
Many types of press plates and texturing/release materials have been used to manufacture high pressure decorative laminate products with a wide variety of surface finishes. Historically, the earliest manufacture was confined to a smooth, reasonably glossy surface finish produced directly from a polished and buffed stainless steel press plate. This finish was sometimes reduced to a dull, essentially smooth, flat finish by rubbing the pressed laminate surface with a slurry of fine pumice. Later on, a lightly textured surface finish was produced by pressing the laminate surface against paper backed aluminum foil xe2x80x9ccaul stocksxe2x80x9d, e.g., kraft paper backed foil Caulstock #6 or litho paper backed foil Caulstock #13, placed between a flat stainless steel backing plate and the laminate, and later stripped off the laminate after the pressing operation. For economic reasons, the aluminum foils were subsequently replaced with specially coated texturing/release papers, usually with proprietary coating formulations based on substituted melamine resins and/or alkyd resins, such as St. Regis"" (now Ivex) LC-55 and LC-58, and S. D. Warren""s Transkote ETL, which produced essentially the same type finish and texture as did the aluminum foils, with a peak-to-valley depth of about 0.0005-0.001 inches. These types of textured finishes became extremely popular, nearly annihilating the glossy finish market, and are still produced in large quantity today, but now most commonly by the use of direct release shot peened or chemically etched stainless steel texturing plates.
Eventually, xe2x80x9clow reliefxe2x80x9d embossed finishes were introduced, for example using the xe2x80x9cheavy inkxe2x80x9d method of U.S. Pat. No. 3,373,068 Grosheim et al., with peak-to-valley depths of about 0.003-0.005 inches. Still later, three-dimensional, deep textured or embossed laminates were manufactured, with peak-to-valley depths of 0.010-0.020 inch or more, for example by the methods of U.S. Pat. No. 3,718,496 issued to Willard and U.S. Pat. No. 3,860,470 issued to Jaisle et al., which are preferred and are incorporated herein by reference. Such laminates, of necessity to retain their mechanical strength, were usually produced substantially thicker than those with conventional xe2x80x9csmoothxe2x80x9d finishes, which adversely affected their postforming capability and often relegated such products to general purpose xe2x80x9cflat stockxe2x80x9d applications. This is especially true as the extent of embossing increased in severity.
Finally, the deep textured laminate technology evolved into efforts to faithfully simulate xe2x80x9cnaturalxe2x80x9d materials such as slate, marble, sandstone, pebbles, brick, cane, woven jute and hemp, leather, rough hewn and weathered timber, woodgrains, tile, and the like. To do so properly, and create a truly natural appearance and texture, registered embossed methods were developed in which the design color contrasts are in register with the peak and valley topography of the texture embossment itself. The earliest xe2x80x9coverlay methodsxe2x80x9d of U.S. Pat. No. 4,092,199 issued to Unger, et al. and U.S. Pat. No. 4,093,766 issued to Scher, et al. relied on use of a pigmented, high flow melamine-formaldehyde resin impregnated overlay placed over a conventional solid color or printed pattern sheet to achieve the registered embossed effect. The later methods of U.S. Pat. No. 4,374,866 issued to Raghava and U.S. Pat. No. 4,376,812 issued to West replaced the pigmented melamine-formaldehyde resin treated overlay with a pigmented melamine-formaldehyde resin coating directly on the treated decorative paper of choice. However in the practice of the instant invention, for the manufacture of a registered embossed, deep grout, tile design high pressure decorative laminate, the method of U.S. Pat. No. 4,092,199 issued to Ungar, et al. is preferred and is incorporated herein by reference.
Over the ensuing years since development of the deep textured embossed and registered embossed high pressure decorative laminate technologies noted above, there have been encountered heretofore insurmountable difficulties in producing a suitable deep textured tile design laminate, particularly one with commercially acceptable postforming properties, because of both the unique geometry of the tile profile itself, and the materials used in its manufacture. Most of the xe2x80x9cnatural materialxe2x80x9d deep embossed designs, whether registered or non-registered, such as a slate or leather pattern, have a random texture with relatively gradual peak-to-valley texture gradients. Conversely, a tile design, and particularly its grout lines, have steep, nearly perpendicular profiles, which with a desirably deep grout, would make the laminate very difficult to handle during processing and fabrication, and in the worse case, the grout could actually punch through the back of the laminate, resulting in shearing and breakage in the press.
Another difficulty in producing an acceptable tile design heretofore is that traditional ceramic tiles are square, and the consumer""s expectation of a tile texture laminate would be that it have square tiles as well. Use of the conventional texturing process of U.S. Pat. No. 3,718,496 issued to Willard, which is widely practiced in the industry, to produce such tile textured laminate, where a real ceramic tile and cementaceous grout artwork master would most likely be used to produce a phenolic resin/kraft paper negative image texturing plate laminate, which in turn could be used to produce the final decorative laminate product, would result in smaller, rectangular tiles. During each step in such a process, i.e., during preparation of the phenolic/kraft texturing plate, during repeated usage of said plate, and during press curing of the final laminate product itself, cumulative asymmetric shrinkage occurs, with shrinkage about twice that in the less paper fiber reinforced crosswise direction of the laminate compared to the more highly reinforced lengthwise direction, due to the paper""s directionality. Of particular concern is the progressive shrinkage of the phenolic/kraft texturing plate with repeated usage, resulting in variable, rectangular tile dimensions, which would make butt joining and mitering of laminates pressed from such texturing plates of differing ages impossible without grout line misalignment.
U.S. Pat. No. 3,860,470 issued to Jaisle et al. recognized the propensity for such phenolic/kraft texturing plates to shrink, and taught preshrinking them with exposure to heat in an oven to stabilize them prior to trimming to plate size and use. This was done strictly to reduce shrinkage during subsequent repeated press use, and therefore increase their useful life before being retired as undersized. With random textures such as a slate or leather design, the fact that the texture itself was also shrinking and changing along with the plate""s overall dimensions was of little consequence in terms of significantly affecting the design aesthetics, joinery capability, etc., as would be the case with a tile design. While such a method of preshrinking would largely resolve the plate age variability problem, it could not resolve the out-of-squareness issue if starting with real ceramic tile artwork.
Thus, for example, a stable, slightly rectangular tile design stainless steel texturing plate with the requisite negative image of the final laminate tile design, which would compensate for the shrinkage of the final laminate product, would be effective in preventing the above-described problems. However, producing such plates, with a raised grout pattern and tile face texture design as well, by mechanical machining, chemical etching or some other method, would be extremely difficult and expensive to accomplish, particularly in any large quantity required to satisfy the capacity of a conventional multi-opening laminating press.
Thus, there is a need for a deep embossed tiled design high pressure decorative laminate that has the characteristics that have not heretofore been achieved. There is also a need for a method of producing such a deep embossed tiled design high pressure decorative laminate. Other needs will become apparent upon a reading of the following detailed description, taken in conjunction with the drawings.
The aforementioned needs are fulfilled by a deep embossed high pressure decorative laminate having a plurality of integral tiles with various surface textures bordered by deep embossed portions. Each tile of the laminate has a peripheral thickness greater than the thickness of the non-peripheral portions of the tile. Preferably, each tile has a concave profile along its upper surface when viewed in cross section. A method of producing artwork necessary for the deep embossed high pressure decorative laminate of the present invention comprises assembling a first layer of fibrous sheets impregnated with a thermosetting resin, a second layer comprising a plurality of adjacent tiles comprising a plurality of fibrous sheets impregnated with a thermosetting resin, wherein the tiles were previously pressed and heated, and a third layer comprising a plurality of shims. The assembly is then pressed and heated against a rigid substrate whereby the second layer forms a substantially convex shape on the upper surface of each tile, thus imparting substantially concave impressions on the first layer. The first layer is subsequently removed from the second and third layers, and grooves are formed in the first layer, preferably by machining.